Regenerated cellulose structures and process for producing them



Nov. 18, 1958 N. cox 2,860,480

REGENERATED CELLULOSE STRUCTURES AND PROCESS FOR PRODUCING THEM Filed April 18, 1956 I INVENTOR NORMAN LOU/S COX ATTORNEY 2,8otl,480 I REGENERATEI) JELL ULGSE'STRUCTURES AND PRGCESS FUR PRODUCING THEM Norman Louis Cox, Wilmington, Del., assignor to E. I.

du Pont de Nemours and Company, Wilmington, Del.,.

This invention relates to the manufacture of regenerated cellulose structures and more particularly to the manufacture of novel high strength viscose rayon filaments, fibers, yarns and cords. This application is a continuation-in-part of application Serial No. 280,169 filed April 2, 1952, now abandoned.

The importance of viscose rayon cords for reinforcement of automobile tires is well known. One of the persistently sought objects in this field is to increase the tenacity of the cords. The cords are composed of a plurality of yarns twisted together. To increase cord tenacity, the prior art has concentrated on increasing the tenacity of the yarns which make up the cords. However, it has now been found that yarn tenacity, which is a longitudinal property of the yarn, is only part of the answer to increased cord tenacity. It is also necessary to improve the transverse properties of the yarn. Because the yarns are highly twisted together to form the cords, the transverse properties of the yarn contribute significantly to the longitudinal properties of the cord.

Efforts to depict the structure of the yarn, or more accurately the filaments that make up the yarn, that will ofier the most advantageous combination of longitudinal properties (tenacity) and transverse properties (those properties which become significant in a highly twisted structure) have met with limited success. One method involves dyeing a cross-section of the filament and examining the dyed cross-section under high magnification. This method is described -in an article entitled Skin Efiect in Viscose Rayon by Morehead and Sisson 1 except for the substitution of Pontamine yellow dye for Calcomine yellow dye. From this work, it was found that a cross-sectional area composed primarily of skin compared to a minimum of core is desired. In practice, this is accomplished by retarding the coagulation. of the viscose filament during spinning. In effect this means that the acidic coagulating bath diffuses more slowly into the interior of the filament while the dilfusion of water and alkali from the filament is not impeded. This results in a more uniform coagulation of the filament with a consequent improvement in quality of the yarn and cord made therefrom. This improved uniformity is manifested, when the filament cross-section is examined by the above-mentioned dyeing technique, by a thick skin and in some cases the filament may appear to be all skin. In addition, the filament contour is generally much smoother, the fine crenulations which are characteristic of thinskinned filaments being substantially absent. In general, a filament composed of at least 75% skin provides substantial homogeneity throughout the filament cross-section. This, it has been discovered, is a neces sary but not a sufficient condition in providing the most desirable filaments.

The sufficiency requirements depend on an even finer examination of the filament structure. The art has recog nized that cellulose filaments are composed of two por- 1 Textile Research Journal, 15, 444-445 (1945).

States atent O tions; (1) a relatively high ordered crystalline portion which can be measured by X-ray examination, and (2) an amorphous area which until recently could not be characterized by any simple measurement. The characteristics of the crystalline portion, which are obtained by X-ray measurement, are associated primarily with the longitudinal properties of the yarn. The two characteristics which have been used by the art in evaluating the crystalline portion of the filament are the lateral order and the orientation.

Lateral order is related to the crystallinity in the structure and is given by the expression:

where I is the 101 interference intensity and I is the minimum intensity between 101 and 101 interferences. Orientation describes the directional arrangement of the crystallites in the filaments. A complete picture of the orientation can be calculated, by procedures described by W. A. Sisson in Industrial Engineering Chemistry, Anal. Ed. 5, 296 (1933), from interference intensities with the orientation value representing that fraction of the interference intensity having a designated orientation. Sisson, in Textile Research 7, 425-431 (1937:), developed a simpler method for providing an orientation value which involves measuring the angular width at half maximum intensity along the arc of an interference on the X-ray pattern. In the present application, the orientation value is expressed as 180 divided by this angular width, utilizing the 101 plane in order to provide a parameter which increases with the orientation, as described by H. G. Inger-sell in Journal of Applied Physics 17, 924 939 where A is the angular width in degrees at half maximum intensity of the 101interference. While high lateral order values and high orientation values are associated with high yarn tenacities (longitudinal properties), it is now recognized that there is a maximum lateral order, above which there is a decided adverse effect on transverse properties. However, there is no such upper limit for the orientation value. As far as orientation is concerned, the higher the better.

Characterizing the amorphous portion of the structure cannot be done by X-ray measurements, but is determined thermodynamically by measuring the change in retractive force when a slightly extended wet filament is held at constant length and subjected to a temperature change ranging from 0100 C. The details of this technique are presented in an article by Roseveare and Poore in the Journal of Polymer Science, 14, 341-354, (1954) As indicated by the authors, the entropy of stretching is the negative of the slope of the force-temperature curve. The minimum point in this curve is the point at which the entropy of stretching decreases to zero as the temperature increases. Desirable transverse properties are only present in those filaments which display force-temperature minima which are below C. This is explained by the following analysis:

In the measurement of force at constant length as a function of temperature, as the temperature is raised vibration of valence bonds increases giving a normal expansion of the material. This expansion in the longitudinal direction causes the retractive force of the slightly stretched yarn to decrease. At higher temperatures thermal motion of segments of the chains becomes appreciable and this motion tends to shorte'n the distance between the ends of the chains, i. e., the chains tend to stant length increases.

coil up, and the force required to hold the yarn at con- A comparison with the forcetemperature curve of rubber shows that rayons have a glass-like behavior below the minimum and rubber-like behavior above. All yarns undergo thermal expansion; however, the ability of the polymer chains to coil at higher temperature depends on their configuration with respect to the neighboring chains which is in turn determined by the structure of the amorphous area. The absence of a minimum below 95 C. with certain yarns is due to the chains in the amorphous areas being highly oriented so that they are held rather rigidly due to the strong attraction of parallel chains. Such yarns would be expected to exhibit the poor transverse properties which are actually observed. While the foregoing explanation probably representsa slight over-simplification of the factors responsible for the shape of the forcetemperature curve, it is presented as a working hypothesis which illustrates the value of the measurement.

Although it is essential that the force-temperature minimum point fall below 95 C. to insure good transverse properties, the desired high level of strength is not achieved if the minimum point is too low. To obtain the optimum balance of properties in a high tenacity yarn, i. e. high strength combined with good transverse properties, the force-temperature minimum point should fall in the range of 60 C.95 C.

The object of the present invention is to provide a novel regenerated cellulose filament having an optimum combinaiton of transverse and longitudinal properties so that it can be formed into a regenerated cellulose cord of substantially high tenacity. A further object is a process for producing such novel regenerated cellulose filaments. Other objects will appear hereinafter.

The objects are accomplished by a regenerated cellulose filament having a cross-sectional area composed of at least 75% skin; being characterized by a lateral order of 15-40, an orientation value above 12 and a minimum point in the force versus temperature curve between 60 C.95 C. Yarns composed of a plurality of such filaments display exceedingly high tenacities, which tenacity persists to a great degree when the yarns are plied into cords, the cords having tenacities of at least 4.5 grams per denier.

Referring to the drawing:

The drawing is a microscopic view of a dyed cross-section of a regenerated celluloss filament of the invention.

The tenacity which persists in the ultimate cord after the conversion of yarn to cord will depend on the twist imparted to the yarn, the twist imparted in plying the yarns together to form the cord and the diameter of the cord. By a cord having at least 4.5 grams per denier is meant a cord formed by plying a yarn into a 2-ply cord having a cord twist multiplier of about 7.3, i. e. from 7.3 to 7.6. More specifically, the procedure for determining cord tenacity consists of twisting a single strand of yarn a given number of turns per inch (TPI) in one direction, the amount of twist imparted to the yarn being equal to or up to 4 TPI greater than the subsequently applied cord twist; plying and twisting two such single yarns into a 2-ply cord by twisting in the opposite direction; and measuring the denier of the final cord. The cord twist multiplier, which must be about 7.3 is obtained by substitution in the expression:

TPI 0.0137 square root of the denier The tenacity of the cord is then measured in the conventional manner.

The process for producing the filaments comprises preparing a viscose solution containing 4%7% cellulose and 4%8% alkali, calculated as sodium hydroxide, using at least 50%, based on the cellulose content of the alkali cellulose, carbon disulfide to give a gamma number greater than 75; extruding the viscose solution having a gamma number of at least 75 through a spinneret into 4 a primary bath containing 4%12% sulfuric acid, 5%- 25% sodium sulfate and 3%l5% zinc sulfate, which bath is maintained at a temperature of at least 40 C., in the presence of a compound selected from the group of compounds given below, the quantity of said compound being sufiicient to reduce the gel swelling of the filaments at least 10%, preferably at least 15%; passing the filaments through the primary bath while controlling the rate of regeneration so that the filaments upon leaving the primary bath have a gamma number of about 18 to about 50; passing the filaments through a hot aqueous secondary bath maintained at a temperature of 50 C. to

the boiling point of the bath; stretching the filaments from to 200%, preferably %l80%, of the unstretched length of the filaments in the secondary bath and reducing the gamma number of the filaments at least 50%, preferably at least 75% in the secondary bath.

The compounds, which for convenience are termed coagulation modifiers and which serve to reduce the gel swelling of the filaments, are present in relatively small amounts, about 0.1 millimole to about 10 millimoles per 100 grams of solution, preferably in the viscose solution. However some of these compounds may be present only in the primary bath, or in both the primary bath and the viscose solution. Agents of. the various chemical classes listed below, when added to the viscose solution, must also fulfill the requirement of being soluble in the viscose, since it has been found that, if solubility is incomplete, or, in other words, if an emulsion or dispersion of the agent in the viscose is present, the desired results are not obtained. For good results, it has been found that the coagulation modifier should be soluble in 6% aqueous sodium hydroxide to the extent of at least 0.05%. Agents having a solubility above this limit are sufiiciently soluble in viscose to give the desired effects. The group of compounds which has been found suitable for use in the process of this invention include the following:

A. Quaternary ammonium compounds of the formula wherein the Rs are organic groups which contain no more than four aliphatic carbon atoms, at least three of the said groups containing only aliphatic carbon atoms and the fourth of the said groups containing no more than one phenyl radical, and where X is an anion having substantially no surface activity. The use of these compounds is disclosed and claimed in U. S. Patent 2,536,014.

B. Aliphatic monoamines having at least four carbon atoms but containing no radical of more than six carbon atoms. The use of these compounds is disclosed and claimed in U. S. Patent 2,535,044.

C. Aliphatic diamines containing two amino nitrogen atoms separated only by carbon atoms and containing a total of at least three carbon atoms, said diamines having the amino groups attached to aliphatic carbon atoms, any monovalent substituent on the amino nitrogens being alkyl groups of 1 to 6 carbon atoms. The use of these compounds is disclosed and claimed in British Patent 762,772.

D. The salts of N-substituted dithiocarbamic acids. The use of these compounds is disclosed and claimed in U. S. Patent 2,696,423.

E. The others of the formula RO(CH CH O),,R, where R is alkyl or aryl; n is an integer from 1 to 4 inelusive; and R is hydrogen, alkyl or aryl. The use of these compounds as coagulation modifiers is disclosed and claimed in British Patent 741,728.

F. The polyethylene glycols of formula HO CH CH O H,

where n is an integer greater than 3. The use of these compounds is disclosed and 1,162,737.

The gamma number of the viscose solution of the filaments is the degree of substitution of cellulose xanthate multiplied by 100, or expressed another Way, it is the number of xanthate groups per 100 glucose units in the cellulose chain.

The percent reduction in gel swelling is obtained by determining the gel swelling" of'the yarn when the yarn is prepared in the presence of the above-specified coagulation modifiers ('GS andcornparing it to the gel swelling of ayarn obtained by'spinningfilaments under identical conditions except for the omission of the coagulation modifiersfGSg). Specifically, a small sample '(5-10 grams) of the gel yarn is collected on abobb'in without stretch and prior to its entry into the hot aqueous secondary bath. The sample iscentrifuged at 3600 revolutions per minute for 5 minutes and weighed in a closed bottle. The sample is then washed free of acid and salt, dried in an oven at 105 C.-110 'C. andrewei-ghed. The ratio of the first weight, the gel weight, to the final weight, the cellulose weight, provides the grams of gel per grams of cellulose and is referred to as the gel swelling. The percent reduction in gel swelling is obtained by substituting in the following expression:

Controlling the rate of regeneration in the primary spinning bath to effect reduction of the gamma number of the viscose filaments from at least 75 as they enter the primary bath to about 18-50 as they leave the bath may be accomplished in several ways. One method involves adding sodium zincate to the viscose solution prior to extrusion in amounts between 0.4% and 1.5%, preferably 0.5%1.0%. Another involves adding to the primary bath 0.4%2.5%, preferably 0.6%1.0% of formaldehyde. w a g The invention will be more clearly understood by referring to the examples and discussionwhich follow. Cord tenacities are obtained using cord twist multipliers of 7.3-7.6'

claimed in French Patent EXAMPLE I p A viscose solution was prepared in the following manner. Sheets of cotton linters pulp were steeped in 18% sodium hydroxide solution for 60 minutes at a temperature of 25 C. The excess caustic solution was then pressed from the resulting alkali cellulose to give a press weight ratio of 3:1. The alkali cellulose was then shredded in a conventional'type shredder for two hours at a temperature of 275 C. The shredded alkali cellulose was then aged to give a desired viscose viscosity of 50:10 stokes.

After aging the alkali cellulose was charged into a baratte and a vacuum drawn on the baratte to permit introduction of the carbon disulfide without loss. 60% carbon disulfide based on the weight of the air dried pulp (approximately 64% based on the weight of cellulose in the alkali cellulose) was added and the xanthation reaction was then allowed to proceed for 4 /2 hours at 24 C.

After xanthation the cellulose xanthate was charged into a mixing tank containing dilute sodium hydroxide solution and mixed for 2 /2 hours at 5 C. to give a viscose containing 5% recoverable cellulose and 6.5% alkali, calculated as sodium hydroxide. During mixing, 0.15% polyethylene glycol having an average molecular weight of 600 and 0.6% butoxyethanol were added to the viscose. The viscose was filtered and deaerated but ripening was held to a minimum.

The viscose was extruded through a spinneret having 1,000 holes of 0.0025 inch diameter into a coagulating and regenerating bath containing sulfuric acid, 17.5% sodium sulfate, 9.5% zinc sulfate and 0.7% formaldehyde and maintained at a temperature of 55 C. The filaments were passed through a convergence guide and then around a power-"driven roller located in the primary bath at a distance of about 40 inches from the spinneret, and then upward to a second power-driven roller located about 40 inches above the first roller. With the aid of a multi-grooved snubber roller the yarn was given two passes around the second power-driven roll, then under two rollers located 16 inches apart in a trough containing a hot secondary bath consisting of about 2% sulfuric acid at'a temperature of about 95 C. The yarn was then passed successively around third and fourth power-driven rollers located a short distance beyond the secondary bath trough and rotating at a sufiiciently higher speed than the second power-driven roller to stretch the yarn 179% in the secondary bath. The yarn was given two wraps around each of these rollers and a hot secondary bath solution at a temperature of about 95 C. was applied to the yarn on both rollers by means of a jet located above each roller. From the final powerdriven roller the yarn was passed downwardly around and under a freely rotating roller and then upward to a rotating bobbin where the yarn was wound up at a speed of 28 yards per minute in the conventional manner.

The yarn was purified by conventional methods and then subjected to a slashing operation which consisted of stretching the yarn slightly in a hot bath containing a yarn lubricant followed by drying without relaxation. The gamma number of the viscose and yarn was determined at various stages in the process. Results of these tests are shown below.

Some of the yarn, which had a denier of 1070, was twisted 15 turns per inch and then a 2-ply cord of 11 turns per inch was prepared by twisting in the opposite direction;

Properties of the yarn and cord are given in column A of Table 1 below. For comparison, properties of several high tenacity yarns of the prior art are given in columns B, C and D. Yarn B is-aa yarn produced by coagulating the filament in a non-regenerating bath, then stretching about 200% and finally regenerating the yarn by treating with dilute sulfuric acid solution. Yarn C is a yarn pro.- duced by spinning into a concentrated (greater than 50%) sulfuric acid bath and stretching over 200%. Yarn D is a high tenacity yarn produced at 28 y. p. m. spinning speed using a coagulation modifier but without controlling the gamma number in the manner of the present invention. Yarn E was prepared similarly to Yarn A except that the coagulation modifier was omitted.

Table 1 A B C D E Yarn Tenacity*, g. p. d 5. 99 6 5 7.3 5.0 4. Cord Tenacity, g. p. d 5.01 3.9 4. 2 4. 25 65 Lateral Order 35. 00 51.0 40. 0 28.0 35.0 Orieutati0n 13. 00 12. 6 12. 0 11. 6 12. 3 Force-Temp.

5. 00 100. 0 100. 0 50.0 100. 0 Cross Section, Percent Skin 100. 00 -100 50.0 Gamma No., Viscose** 853:5 36.0 65 85:1;5 Gamma No., Yam (1) 30:1:5 30.0 5 30:1:5 Gamma No., Yarn (2) 5-10 5. 0 1 5-10 Percent Reduction in Gel Swelling 22 0 0 20 0 *Tenacity measured at 12% moisture regain. **Vise0se at time of extrusion.

Yarn (1) Just before entering secondary bath. Yarn (2) After secondary bath.

EXAMPLE H The viscose solutions were prepared in the manner described for yarn A of Example I except for the amounts of carbon disulfide and the coagulation modifiers used. The amounts of carbon disulfide used are given in Table 2. However, for yarns G and H, the viscose was ripened to provide gamma numbers below that required by the invention. Yarn F was produced in accordance with the process of this invention. For yarns F, G, and H, the modifier was distributed between the viscose solution and the primary bath, 0.083% N-methylcyclohexyldithiocarbamate being added to the viscose and 0.019% N-methylcyclohexylamine being present in the bath. In preparing yarn J, only 40% carbon disulfide was used in the xanthation and 0.13% N-methylcyclohexyldithiocarbamate was added to the viscose solution in the mixer. Spinning and processing of the yarns were carried out as in Example I. The results are summarized in Table 2.

Table 2 F G H .T

Carbon Disulfide, Percent 53 53 53 40 Gamma No., Viscose 79 62 55 62 Gamma No., Yarn (1)... 31 26 26 23 15 Gamma No., Yarn (2) 12 6 7 l1 Spinning Stretcl1 155 155 138 133 Yarn Tenacity, g. p. d 5. 80 5. 34 5.00 5. 50 Cord Tenacity, 4. 60 4.12 3. 72 4. 23 Lateral Order. 35 35 35 35 Orientatin 12. 11. 5 11. 3 11. 4 Force-Temp. Min. Point, O. 7 80 82 75 Cross Section, Percent Skin 90-100 00-100 90-100 90-100 20 Percent Reduction in Gel Swelling 20 2 2 20 EXAMPLE III Viscose was prepared using 60% CS as described for yarn A in Example I .using 0.15% polyethylene glycol having an average molecular Weight of 600 in the viscose solution. The viscose was extruded into a bath containing 10% sulfuric acid, 17.5% sodium sulfate and 9.5% zinc sulfate and maintained at a-temperature of 55 C. Spinning and processing of the yarn were carried out as described in Example I. Yarn L was prepared without the aid of an agent for controlling the rate of dexanthation while Yarn K was spun into a bath which also contained 0.7% formaldehyde. Results of these tests are A viscose containing 0.2% by weight of polyethylene glycol (average molecular weight 600), 5% recoverable cellulose and 6% alkali, calculated as sodium hydroxide, was prepared as follows:

Alkali cellulose, aged to get the desired viscose viscosity (about 30 stokes), was xanthated for five hours using 62% carbon disulfide, based on the cellulose content of the alkali cellulose. The resulting cellulose xanthate was dissolved in sufiicient dilute sodium hydroxide solution to give the desired composition and mixed for two hours at a temperature below C. During mixing the polyethylene glycol and 0.5% by weight of sodium zincate were added to the viscose. The viscose was filtered, deaerated and held at a temperature of 0 C. until it was spun. When spun the viscose had a gamma number above 80.

This viscose solution was spun into an 1100 denier yarn having 400 filaments by extruding through a spinneret having holes of 0.0025 inch diameter into a primary coagulating and regenerating bath maintained at 60 C. and containing 8.5% sulfuric acid, 14% sodium sulfate and 13% Zinc sulfate. After the primary bath, the yarn was stretched 157% in a secondary bath consisting of 1% sulfuric acid at 95 C.-100 C. and then wound on a bobbin at 28 y. p. In. After the yarn was washed free of 8 acid and salt, it was dried without stretch on a slashing machine.

Properties of the yarn and cord prepared from this viscose are shown in the following table, Table 4, along with other pertinent data on the filaments.

A viscose solution was prepared as described in Example I except that sufficient N-methylcyclohexylamine was added to the sodium hydroxide solution in the mixing tank prior to adding the xanthate to give a concentration in the final viscose of 0.049% by weight. The viscose solution was extruded into a primary bath maintained at 55 C. and containing 10% sulfuric acid, 17.5% sodium sulfate, 9.5% zinc sulfate, 0.7% formaldehyde, and 0.016% N-methylcyclohexylamine. The yarn was passed through a primary bath for a distance of inches and then stretched 144% in a hot secondary bath containing about 2% sulfuric acid at a temperature above C. The yarn was wound on a bobbin at a speed of 28 yards per minute and then purified and slashed as described in Example I. Properties of the yarn and cord and other pertinent data are given in Table 5.

EXAMPLE VI A viscose solution containing 0.15% by weight (0.25 millimole per 100 grams) of polyethylene glycol having a molecular weight of about 600, 5% cellulose and 6% sodium hydroxide was prepared as follows:

Alkali cellulose, prepared substantially as in Example I except that it was not aged, was xanthated for 3 hours using 50% carbon disulfide (based on the bone dry cellulose). The xanthate crumbs were dissolved in aqueous sodium hydroxide. After mixing 1.5 hours at a temperature below 15 C. the polyethylene glycol was added and the mixing was continued for 10 minutes. The freshly prepared viscose was filtered cold and kept at 0 C. until it was spun.

The viscose was spun at a gamma number above 75 into an 1100 denier yarn containing 400 filaments by extruding through a spinneret having holes of 0.0025 inch diameter into a primary coagulating and regenerating bath maintained at 50 C. and containing 10% sulfuric acid, 14% sodium sulfate, 13% zinc sulfate, and 0.75%

formaldehyde. After the primary bath, the yarn was stretched 185% in a secondary bath consisting of 1% sulfuric acid at C.- C. After the gel yarn was washed free of acid and salt, it was dried without stretch ona slashing machine.

The properties of the resulting yarn M and cord are listed in accompanying Table 6, together with those of a control yarn N prepared under essentially the same conditions but in the absence of formaldehyde.

EXAMPLE VII This example shows the elfectiveness of additional types of compounds in the process of this invention. Small amounts of yarn Were spun substantially as described for yarn A in Example I except that the compounds indicated in Table 7 were used. The results were substantially those obtained for yarn A.

Table .7

COMPOUND Hexamethylenediamine 0.03% in viscose, 0.03% in bath Butoxyethanol, 0.6% in viscose Suitable coagulation modifying agents in addition to those mentioned in the examples include the following: i A. Among the quaternary ammonium compounds of the formula wherein the R's are organic groups which contain no more than 4' aliphatic carbon atoms, at least three of the said groups containing only'aliphatic carbon atoms and the fourth containing no more than one phenyl radical, and where X- is an anion having substantially no surface activity, the following may be mentioned: benzyltrimethylammonium hydroxide, tetraethylammonium hydroxide, tetramethylammonium chloride, phenyltrimethylammonium hydroxide, tetraethanolammonium hydroxide, tetraethylammonium bromide, tetramethylammonium iodide, tetrapropylammonium hydroxide, tetrabutylammonium chloride, tributylpropylammonium hydroxide, tri(beta hydroxyethyl) methylammonium hydroxide, tributyl (beta hydroxyethyl) ammonium iodide, etc. The preferred agents of this class are those in which all four organic groups attached to the nitrogen atom are hydrocarbon group orhydroxyl-substituted hydrocarbon groups and in which the radical X is hydroxyl or halogen of atomic weight above 19, i. e., chlorine, bromine or iodine. The most useful modifiers of this group are the quaternary ammonium hydroxides having a total of not more than ten carbon atoms in the molecule and in which all organic groups are hydrocarbon or hydroxyl-substituted hydrocarbon.

B. Among the aliphatic acyclic or alicyclic primary, secondary or tertiary monamines having at least four carbon atoms but containing no radical of more than six carbon atoms may be mentioned triethanolamine, triethylamine, diethanolamine, butylmonoethanolamine, diethylaminoethanol, n-amylamine, diethylamine, dipropylamine, n-butylamine, ethyldiethanolamine, dipropanolamine, propylpropanolamine, hexanolamine, amyldiethanolamine, butylmethylethanolamine, propylethanolamine, cyclohexylethanolamine, hexamethyleneimine, piperidine, hexyldiethanolamine, etc. The preferred modifiers of this group are those in which the amino nitrogen is attached to hydrocarbon groups, preferably alkyl groups, and/ or to hydroxaylkyl groups.

C. Among the aliphatic diamines containing a total of at least three carbon atoms and having the amino groups attached to aliphatic carbon atoms, the amino groups being separated by a chain of only carbon atomsand any monovalent substituent on the amino nitrogen being alkyl groupof 1' to 6 carbon atoms, may be mentioned the following: hexamethylenediamine, tetramethylenediamine, N methyltrimethylenediamine, N,N dimethylethylenediamine, N,N-diisobutylhexamethylenediamine, N,N-dimethyltrimethylenediamine, 4,4-dimethylhexamethylenediamine, N,N-diethyl-l,4-cyclohexanediamine, 3-ethoxyethoxyhexamethylenediamine, pentamethylenediamine, octamethylenediamine, N cyclohexyltetramethylenediamine, N,N diallylhexamethylenediamine, N methylnonamethylenediamine, N hexyltrimethylenediamine, N,N-dimethylpiperazine, N-butylhexamethylenediamine, etc. The preferred agents of this class are the wholly aliphatic, including cycloaliphatic, diamines which contain onlycarbon and hydrogen besides the two amino nitrogens and which have a total number of carbon atoms between 4 and 14, inclusive, in addition to fulfilling the other requirements stated above. Still more preferred are the polymethylenediamines of 4 to 14 total carbon atoms having from 4 to 8 methylene groups between the amino groups, and their N-alkyl substituted derivatives Where the N-alkyl. groups have from 1 to 4 carbon atoms incluslve.

D. Among the salts of N-substituted dithiocarbamic acids may be mentioned, sodium amyl dithiocarbamate, sodium butyl monoethanol dithiocarbamate, sodium hexamethylene bis (dithiocarbamate), potassium pentamethylene dithiocarbamate, sodium methyl dithiocarbamate, sodium benzyl dithiocarbamate, sodium ethylene bis dithiocarbamate), sodium 1,3-cyclohexane bis (dithiocarbamate), sodium dibutyl dithiocarbamate, sodium dimethyl dithiocarbamate, sodium dioctyl dithiocarbamate, sodium lauryl dithiocarbamate, lithium cyclohexyl dithiocarbamate, the sodium dithiocarbamates of a mixture of 10% hexadecylamine, 10% octadecylamine, 35% octadecenylamine and 45% octadecadienylamine, sodium hexamethylene bis (methyl dithiocarbamate), sodium ethylene bis (methyl dithiocarbamate), sodium 1,4-cyclohexane bis' (ethyl dithiocarbamate), sodium xylylene bis (dithiocarbamate), etc. The preferred modifiers of this class are the alkali metal salts of monoor di-N- sub- 'stituted dithio'carbamic acids containing no more than 10 carbon atoms in any radical and in which the nitrogen is attached to aliphatic carbon.

E. Among the ethers of the formula where R is alkyl or aryl, n equals 1,2,3 or 4 and R is hydrogen, alkyl or aryl may be mentioned phenoxyethanol,

ethoxyethanol, methoxyethoxyethanol, butoxyethoxyethanol, phenoxyethoxyethanol, ethoxyethoxyethoxyethanol, butoxyethoxyethoxyethanol, phenoxyethoxyethoxyethanol, butoxyethoxyethoxyethoxyethanol, phenoxyethoxyethoxyethoxyethanol, l-ethenyloxy-Z-methoxyethylene, ethylene glycol diethyl ether, triethylene glycol diethyl ether, tetramethylene glycol diethyl ether, triethylene glycol dimethyl ether, diethylene glycol diethyl ether, etc. With this class of coagulation modifiers, it has been found that only those compounds which, in addition to being soluble in viscose, are diificultly soluble in the coagulating bath, i. e., to the extent of less than 0.5%, give the desired results.

F. The polyethylene glycols of formula modifiers, which may belong to the same chemical class or to different ones. a

For effective results, the modifiers should be preferably used in the viscose, in total concentrations of at least 0.1 millimole per 100 grams of viscose solution. Those compounds listed under headings E and F (ethers and polyethylene glycols as specified) must be added to the viscose solution for successful results. In general, it is unnecessary to use more than 10 millimoles of the agent per 100 grams of solution, a generally useful range being 0.5 to 4.0 millimoles per 100 grams. In terms of the less informative weight percent basis, there should be used between about 0.008% and 1% of the modifying agent. It will be understood that these concentrations depend to some extent on the nature and effectiveness of the compound. For example, it is in general indicated to use a larger amount of a quaternary ammonium compound than of a diamine. The most effective concentration to obtain the desired reduction in gel swelling also depends to some extent on process variables such as the spinning speed, since at the high spinning speeds used in industrial practice less agent is desirable than at lower speeds, for the reason that the rate of coagulation should be retarded only to the extent compatible with complete coagulation during the short time the filament is in contact with the spinning bath. As has already been stated, coagulation modifiers of the types recited have the common property of lowering the gel swelling factor by at least 10% in comparison with the corresponding values for identical, but unmodified, viscose spinning systems. The great majority of these compounds lower the gel swelling factor by over 15%.

The viscoses used in the process of this invention may be of a variety of types. They may be prepared from wood pulp, cotton linters or mixtures of the two, or from other types of cellulose. The composition of the viscose may be varied but within a narrow range. For example, it may have a cellulose content of from 4% to 7% and an alkali content of from 4% to 8%. Viscoses having between 4.5% and 5.5% of cellulose and between 4% and 6% of alkali, are preferably used. The amount of carbon disulfide used in the Xanthation must be above 50% based on the recoverably bone-dry cellulose to provide the high gamma number of at least 75 at the time of extrusion. With viscoses having cellulose contents in the range of 6% to 7%, 60% or more carbon disulfide should be used to give correspondingly high gamma numbers. Xanthation may be carried out in the conventional manner or, if desired, split Xanthation, i. e. addition of part of the carbon disulfide to the viscose in the mixer, as described and claimed in U. S. Patent 2,801,998 filed by A. Robertson on April 28, 1953, may be used.

The invention involves the use of a two-bath spinning system. The coagulation and regenerating primary bath contains sulfuric acid, sodium sulfate and zinc sulfate. If desired, additional salts of divalent metals known to supplement the action of zinc sulfate may be used such as ferrous sulfate, manganese sulfate, nickel sulfate or chromic sulfate, particularly the first named salt. The use of these divalent metal salts makes it possible to use smaller amounts of zinc sulfate than are necessary in their absence. Preferably, the spinning bath contains from 4% to 12% of sulfuric acid, from to 25% of sodium sulfate, and from 3% to 15% of zinc sulfate. The optimum quantity of zinc sulfate from the standpoint of practical spinning speeds, reduction in gel swelling, and extent of modification of yarn properties appears to be 4% to 13%. The temperature range of best spinnability is from 40 C. to 65 C.

During spinning, the rate of dexanthation of the cellulose must be controlled by addition of a stabilizing compound to the viscose or spinning bath so that the yarn has a gamma number of at least about 18 but no higher than about 50 as it enters the hot secondary bath; Yarns having lower gamma numbers are not sufliciently stretchbobbin, bucket, or continuous processes.

able to give the desired properties in the yarn while yarns with higher gamma numbers usually have high gel swellings and are difficult to dexanthate sufficiently in the secondary bath. At least 50% of the remaining xanthate groups and preferably 75% or more should be removed before the yarn leaves the secondary bath. Removal of the xanthate groups in this manner stabilizes the structure and thus preserves the excellent properties achieved by the treatment of the yarn 'up to that point.

Controlling gamma number, as described above, may be accomplished by adding sodium zincate at any stage during the preparation of the viscose solution. The amount used, as stated previously, is preferably between 0.5% and 1.0% Other alkali metal zincates, such as potassium zincate and ammonium zincate are also operable. When formaldehyde is used, it is used in the primary spinning bath itself. It is only necessary to use small amounts of it, in the range of 0.4% to 2.5% by weight of the bath, and preferably between 0.6% and 1.0%. The use of more than 2.5 of formaldehyde in the spinning bath is undesirable since the gamma number remains too high and the yarn becomes too highly plasticized. The optimum amount of formaldehyde varies somewhat with the spinning speed, more of it being desirable at the higher speeds.

After leaving the coagulating and regenerating bath, the filaments are passed through a secondary bath (hot dip bath, or stretching bath) wherein most or all of the stretch 'is applied. The secondary bath may consist simply of water or of dilute (1%3%) sulfuric acid, or

it may have the same composition as the coagulating bath but at a greater dilution, e. g., one-fourth of the concentration of the coagulating bath. The temperature of the secondary bath should be at least 50 C., and for the best results it is preferably between C. and the boiling point of the aqueous solution used. The preferred procedure is to draw off the the freshly coagulated gel yarn with a feed wheel speed equal to or less than the jet velocity and to apply all the stretch in the secondary bath between positively driven rollers traveling at different speeds. For producing high tenacity yarns, stretch is applied in the secondary bath to the extent of 120%200% of the unstretched length of the yarn.

The final feed wheel speed or wind-up speed or, as more commonly called, the spinning speed was 28 yards per minute in the examples. However, the process of this invention is not so limited but may be operated below this speed or above, commercial spinning speeds ranging up to yards per minute or higher. It should be understood that the exposure of the filaments to the primary bath (travel within the bath plus any travel in air wherein the filaments carry bath on their surfaces) is usually at least three seconds. For instance, in a process where the spinning speed is 28 yard per minute and the spinning stretch ranges from %-200%, it is preferred to expose the filaments to the primary bath solution for a distance of at least 30 inches. This exposure corresponds to an exposure time of 3.9 seconds.

The bobbin process has been used in the examples but it is immaterial Whether the spinning is done by the The yarn is washed free of acid and salt by conventional methods and then dried under tension, according to known procedures. If preferred, the yarn may be tw'isteror slasher-dried to enable the dry elongation of the finished product to be controlled.

Spinning may be carried out with the aid of spinning tubes such as are described in Millhiser U. S. Patent 2,440,057 or in Drisch et al. U. S. Patent 2,511,699. These tubes of relatively small diameter and of substantial length confine the filaments in their critical stage It is thus possible to increase materially the rate of spinning without any substantial sacrifice in the properties of the product.

The novel filaments produced by the process of this invention have been described. When they are formed into cords, outstanding cord tenacities are obtained. These filaments are particularly desirable for use in the tire cord industry because of the unique combination of longitudinal and transverse properties, but they have outstanding merits for any purpose where regenerated cellulose fibers are finding applications, such as in the textile industry.

As many different embodiments of the present invention may be made without departing from the spirit and scope thereof, it is to be understood that theinvention is not limited except to the extent defined in the appended claims.

What is claimed is:

l. A regenerated cellulose filament having a crosssectional area composed of at least 75% skin, the remainder being core; when subjected to X-ray examination, said filament being characterized by a lateral order of 15-40 and an orientation value above 12; and said filament displaying a minimum point in the force versus temperature curve between 60 C. and 95 C.

2. A regenerated cellulose yarn composed of a plurality of the regenerated cellulose filaments described in claim 1.

3. A cord composed of a plurality of regenerated cellulose yarns described in claim 2, said cord having a tenacity of at least 4.5 grams per denier when formed by plying two yarns into a 2-ply cord having a cord twist multiplier of about 7.3.

4. A process for producing regenerated cellulose filaments which comprises preparing a viscose solution containing 4%7% cellulose and 4%3% alkali by using at least 50% carbon disulfide based on the cellulose content of the alkali cellulose; extruding said viscose solution through a spinneret, said viscose solution having a gamma number of at least 75, into a primary bath containing 4%-12% sulfuric acid, 5%25% sodium sulfate and 3%15% zinc sulfate, said bath maintained at a temperature of at least 40 (3., said extrusion occurring in the presence of a compound which reduces the gel swelling of the filaments at least passing the filaments through the primary bath while controlling the rate of regeneration of the viscose filaments so that said filaments upon leaving the primary bath have a gamma number of about 18 to about 50; passing the filaments through an aqueous secondary bath maintained at a temperature between 50 C. and the boiling temperature of the bath; stretching the filaments from 120%-200% of the unstretched length of the filaments in the secondary bath and reducing the gamma number of the filaments by at least 50% in the secondary bath.

5. A process as in claim 4- wherein the compound for reducing gel swelling of the filaments at least 10% is selected from the group consisting of quaternary ammonium compounds of the formula wherein the Rs are organic groups which contain no more than four aliphatic carbon atoms, at least three of the said groups containing only aliphatic carbon atoms and the fourth of the said groups containing no more than one phenyl radical, and where X is an anion having substantially no surface activity; aliphatic monoamines having at least four carbon atoms but containing no radical of more than six carbon atoms; aliphatic diamines containing two amino nitrogen atoms separated only by carhon atoms and containing a total of at least three carbon atoms and having the amino groups attached to aliphatic carbon atoms, any monovalent substituent on the amino nitrogens being alkyl groups of 1 to 6 carbon atoms; salts of N-substituted dithiocarbarnic acids; ethers of the formula RO-(CH CH O),,R, where R is a member selected from the group consisting of alkyl and aryl, n is an integer of from 1 to 4 inclusive and R is a member selected from the group consisting of hydrogen, alkyl and aryl; and polyethylene glycols of the formula IIO(CH CH O) H, where n is an integer greater than 3.

6. A process as described in claim 5 wherein about 0.1 millirnole to about 10 millimoles of said compound per grams of viscose solution is added to the viscose solution prior to extrusion.

7. A process as in claim 4 wherein the means for controlling the rate of regeneration of the viscose filaments comprises adding from 0.4% to 1.5% sodium Zincate to the viscose solution prior to extrusion.

8. A process as in claim 4 wherein the means for controlling the rate of regeneration of the viscose filaments comprises adding from 0.4% to 2.5% formaldehyde to the primary bath.

References Cited in the file of this patent UNITED STATES PATENTS 2,452,130 Kayser Oct. 26, 1948 2,535,044 Cox Dec. 26, 1950 2,536,014 Cox Dec. 26, 1950 2,696,423 Dietrich Dec. 7, 1954 2,703,270 Studer et al. Mar. 1, 1955 

1. A REGENERATED CELLULOSE FILAMENT HAVING A CROSSSECTIONAL AREA COMPOSED OF AT LEAST 75% SKIN, THE REMAINDER BEING CORE, WHEN SUBJECTED TO X-RAY EXAMINATION, SAID FILAMENT BEING CHARACTERIZED BY A LATERAL ORDER OF 15-40 AND AN ORIENTATION VALUE ABOVE 12; AND SAID FILAMENT DISPLAYING A MINIMUM POINT IN THE FORCE VERSUS TEMPERATURE CURVE BETWEEN 60*C. AND 95*C. 